Pad printing, also called cliche printing, is a printing method originally developed for printing watch faces. It has evolved into an industrial printing process used to print three-dimensional items of all kinds from golf balls and doll faces to candy and pharmaceuticals. Although industrial pad printers are beyond the reach of most DIY-ers in terms of cost and complexity, some manufacturers produce hobby machines suitable for small-volume work.
Pads And Processes
Pad printing uses silicone rubber pads to transfer ink from the printing plate onto the item. Pads come in all shapes, sizes, and durometers -- hardness levels -- to suit the particular item. When the inked pad is pressed onto the item, it forms perfectly into shallow recesses, such as a golf ball or doll-face, or contoured smooth surfaces, such as coated candy, pills, or cell phone faces. The silicone material allows ink to transfer cleanly from the pad to the item.
Pad printing plates are made of metal and can be computer engraved or photo-developed using special plate processors. For the DIY-er, photopolymer plates are inexpensive, and easily developed with the proper platemaking device. The printed design is etched slightly below the surface, which allows the design to hold ink for pickup by the pad.
Inking of the plate is done by metal ink rollers, which apply ink over the entire plate surface. A metal strip, called a "doctor blade" is then applied to the plate. The doctor blade scrapes the excess ink from the plate surface, but leaves the ink in the engraved image area. Special pad printing ink formulations are used, mixed by the printer, with a combination of ink, thinner, drying retarder and hardener.
Pad printing presses are designed to hold and apply ink, the plate, item, pad and doctor blade. While every press operates differently, the basic process is as follows: The item is placed in a holding jig. The operator cycles the press to ink the plate and apply the doctor blade. The pad is moved onto position over the plate, pressed down to receive the ink, moved over to the item, and pressed onto the item to deposit the ink. DIY-ers should investigate all press types, and choose one that is fully adjustable, and facilitates all of the operations within the confines of the machine. Machines that require the printer to apply ink or doctor blade manually should be avoided.
Do It Youself
Even the simplest pad printing presses are heavy-duty, and engineered to close tolerances to allow repeatable results. The highly specialized pad, plate, ink and inking system used in the process are developed and manufactured only for pad printing use, making substitutions and shortcuts impossible. Although the process is simple in theory, much experience is necessary for good results. The plate and ink formulation are the two most important parts of the process, and instructions must be followed to the letter. Equipment and supply manufacturers and distributors are excellent sources of advice and knowledge, but the basics of the process are best learned through professional training, books or videos.